This invention relates to a video/audio compressing device for recording a compressed video code and a compressed audio code in a recording medium such as a CD-ROM and hard disk and to a video/audio reproducing device for use in reproduction of a recorded video code and a recorded audio code.
A video/audio reproducing device reads video and audio codes recorded in a recording medium such as a CD-ROM and a hard disk and provides a reproduction on a display or a speaker. The video and the audio codes to be reproduced by the video/audio reproducing device are compression-coded and recorded by a video/audio compressing device.
An interframe difference encoding method has been widely applied to such a conventional video/audio compressing device of the type described.
In the interframe difference encoding method, a difference value is compression-coded by the use of the fact that difference values between video frames concentrate around zero. A video signal is separated into a luminance signal and a color difference signal. Differential values between picture elements of a current frame and a preceding frame are calculated and compression-coded. A plurality of frames are compressed by successively compression-coding the difference values. Since the difference value between frames my become large due to a scene change, those frames (key frames) encoding values of the picture elements, not the difference values, are inserted at a predetermined interval.
The above-mentioned system requires a device capable of editing, comprising, and recording a large amount of video and audio information at a high speed. Upon reproduction, the audio information is reproduced in combination with the video information corresponding thereto. Accordingly, the timing (synchronization) of reproduction must be adjusted. Particularly, due to the capacity of the device and the size of the compressed video code, a video recording/reproducing rate may be slower than an audio recording/reproducing rate. This results in collapse of synchronization between the video and the audio upon reproduction. In this event, an unnatural impression is given to a watcher of the display.
In order to prevent the collapse of synchronization, several attempts have been proposed. An example for establishing the synchronization is disclosed in Japanese Patent Prepublication No. 274480/1986. In this system, varied picture elements are detected and clear videos successively derived from rough videos are encoded. Thus, high-speed video compression/reproduction is attained. Another example is also disclosed in Japanese Patent Prepublication No. 117290/1988, the video is divided into a plurality of regions. Particular regions with any change alone are encoded to achieve high-speed video compression/reproduction.
Thus, in the conventional video/audio compressing device or video/audio reproducing device, the videos are partially subsampled to simplify the video processing so as to achieve high-speed video compression/video reproduction.
However, as those regions containing an increased number of varied picture elements alone are encoded, large-motion regions are properly reproduced but small-motion regions are not reproduced. As a result, it is inevitably caused to happen that the motion of a whole scene seems unnatural.